In conventional internal combustion engines, the heat transfer rate to an engine block from a bore in which a piston reciprocates varies along the length of the bore. As a result the temperature of the engine block and degree of expansion may vary along the length of the bore. Such variation may affect the seal between a piston and the bore and may affect the performance of the engine.
Furthermore, during warm up of an internal combustion engine, the engine block structure acts as a large heat sink because the thermal inertia of the engine block structure is an order of magnitude greater than the coolant and oil. As a result, the engine block structure takes longer to warm up than the oil. By way of example, oil returning from a cylinder head of the engine has been heated and loses heat as it returns through the engine block to an oil sump. The resulting colder oil has a higher viscosity, which leads to higher friction losses. This in turn leads to worse fuel consumption.
Moreover, the drive for greater fuel economy and lower CO2 emissions for motor vehicle engines has resulted in smaller and lighter engines, turbochargers, direct injection and exhaust gas recirculation. However, these developments generate more heat. As a result of the additional heat generated by a modern turbocharged engine, a separate oil cooler is required to prevent the engine oil from degrading at the higher temperatures. However, the oil cooler and associated hardware add weight, complexity and cost to the vehicle. Furthermore, the oil cooler acts as an additional heat sink in the oil circuit. This additional thermal inertia slows down the warm up of oil that is delivered to the working parts of the engine.